Finger (U.S. Pat. No. 4,218,400), herein incorporated by reference, has recited oxidizing fluorene to fluorenone by air or oxygen, in the presence of a quaternary salt in a two-phase system, containing a water-immiscible solvent and aqueous alkali metal hydroxide solution.
Kinoshita et al., "Liquid Phase Air Oxidation of Fluorene. Part 1. Effects of Alkali and Pyridine," Nippon Kagaku Zasshi, vol. 80 (1959), pages 206-208, have proposed oxidation of fluorene to fluorenone in a mixed solution of pyridine and aqueous sodium hydroxide solution (about 1N) at about 95.degree. C. The conversion to fluorenone is of the order of 50 percent.
Pearson et al. (U.S. Pat. No. 4,009,151), herein incorporated by reference, have proposed the oxidation of 2-vinylfluorene to 2-vinylfluorenone in a dilute solution in pyridine, containing a small amount of benzyltrimethyl ammonium chloride.
Niznik (U.S. Pat. No. 3,875,237) has proposed preparing fluorenone from fluorene by oxidation with molecular oxygen in dimethylsulfoxide, using a small amount of an alkali metal hydroxide, at temperatures from ambient to about 100.degree. C.
Hiiro et al. (JP Kokai 79/144,348, Chem. Abs. 92:215069q) have proposed oxidizing aromatic or heterocyclic methylene compounds, including diphenylmethane, anthracene and fluorene, in the presence of alkali in 1,3-dimethylimidazolidinone.
Sprinzak, "Reactions of Active Methylene Compounds in Pyridine Solution. I. The Ionic Autoxidation of Fluorene and its Derivative, J. Am. Chem. Soc., vol. 80 (1958), pages 5449-5455, have disclosed oxidation of fluorenes to fluorenones in pyridine solution in the presence of benzyltrimethyl ammonium hydroxide.
Szeverenyi et al. (HU 198,668B) have proposed preparing 9-fluorenone from fluorene by oxidation with air or oxygen in a solvent in the presence of a quaternary ammonium salt and potassium hydroxide at low temperatures.
Knoche (FR 2,142,217, Chem. Abs. 79:50398a) recites the oxidation of fluorene to fluorenone in the presence of a saturated solution of KOH or NaOH in polyether solvents.
Ma (U.S. Pat. No. 4,297,514), herein incorporated by reference, recites the oxidation of compounds, having activated methylene radicals in a multiphase system containing a synergistic combination of elemental carbon and a phase-transfer catalyst.
Although the processes disclosed heretofore give oxidation products, there is a continuing need for processes for oxidizing fluorenes to fluorenones, characterized by high reaction rates, high yields and ease of separating the thus-produced fluorenones. In particular known methods of oxidizing fluorene to fluorenone are not selective for fluorene when the fluorene starting material is impure, containing other oxidizable hydrocarbons, e.g. diphenylmethane. When compounds other than fluorenone are produced in such oxidations, separation from fluorenone is difficult. It would, therefore, desirable to have an oxidation process selective for formation of fluorenone.
It an object of this invention to provide a fast, selective process for making fluorenones from fluorene, wherein the thus-produced fluorenones are readily isolated from the reaction mixtures.